Keeping in step with an increase in the number of pixels per unit area in solid state image sensors represented by CCD image sensors and CMOS image sensors, the pixel size is decreasing in recent years. As a consequence, the number of photons that enter each pixel has decreased to lower the sensitivity so that a reduction in S/N may arise.
Further, in the currently wide-used structure that each pixel is covered by a color filter of one of R (red color), G (green color), and B (blue color), a loss arises in terms of sensitivity because in a red pixel, for example, green light and blue light do not transmit through the color filter and are not used in photoelectric conversion. In addition, a color signal of only one of R, G, and B is available from each pixel so that interpolation processing is conducted among pixels. However, false colors may be produced upon such interpolation.
As a measure for resolving these problems, there is known an image sensor structure in which three layers of photoelectric conversion sections are stacked in a vertical direction for each pixel so that photoelectrically-converted signals of the three colors can be obtained at each pixel. Specifically, a structure has been proposed in which, for example, an organic photoelectric conversion film corresponding to G light is provided over a Si substrate, and PDs (photodiodes) which correspond to B and R individually are stacked in the Si substrate (see, for example, PTL 1 or 2).
In the above-mentioned structure, it is necessary to transfer charges from the organic photoelectric conversion film above the Si substrate to an FD (floating diffusion) formed on an opposite side of the Si substrate. A structure has, therefore, been proposed in which a through-electrode for each pixel is formed extending through a Si substrate and charges are transferred from the organic photoelectric conversion film to the FD via the through-electrode (see, for example, PTL3).